There are a multiplicity of transmission modes both new and old at the disposal of a radio amateur, but the leader of the pack is still single-sideband or SSB. An SSB transmitter emits the barest minimum of RF spectrum required to reconstitute an audio signal, only half of the mixer product between the audio and the RF carrier, and with the carrier removed. This makes SSB the most efficient of the analog voice modes, but at the expense of a complex piece of circuitry to generate it by analog means. Nevertheless, radio amateurs have produced some elegant designs for SSB transmitters, and this one for the 80m band from [VK3AJG] is a rather nice example even if it isn’t up-to-the-minute. What makes it rather special is that it relies on only one type of device, every one of its transistors is a BC547.
In design terms, it follows the lead set by other simple amateur transmitters, in that it has a 6 MHz crystal filter with a mixer at either end of it that switch roles on transmit or receive. It doesn’t use the bidirectional amplifiers popularised by VU2ESE’s Bitx design, instead, it selects transmit or receive using a set of diode switches. The power amplifier stretches the single-device ethos to the limit, by having multiple BC547s in parallel to deliver about half a watt.
While this transmitter specifies BC547s, it’s fair to say that many other devices could be substituted for this rather aged one. Radio amateurs have a tendency to stick with what they know and cling to obsolete devices, but within the appropriate specs a given bipolar transistor is very similar to any other bipolar transistor. Whatever device you use though, this design is simple enough that you don’t need to be a genius to build one.
Via [G4USP]. Thanks [2ftg] for the tip.
Is that an actual PCB? I thought those were against the homebrew code of conduct.
Where are you seeing that? I just see perfboard or something similar. Haven’t seen any printed traces.
I was prepared to be seriously impressed, then I remembered my car only has one wheel and one piston.
a unicycle?
Giga HZ capable transistors are equally cheap if you want to use such a design for wavelengths shorter than 8 London buses.
Many many years ago I built an FM transmitter, it also used BC547 only (2 for the mic amp and one as oscillator). I would consider 100MHz (3m) slightly shorter than 8 London buses :-)
You are right, GHz transistors are not expensive any more. But you do not want too excessive frequency capability in your devices to avoid parasitic oscillations. Because then you wonder why your transistor gets hot while you do not see anything on your scope. But you just do not have the equipment to measure or see the GHz oscillation.
True, mentioning GHZ was for exemplification only. I’ve always been amazed by hams with their seemingly wizardly electronics skills, taming the unmeasurable, but this day and age, building a receiver has become very accessible with IC building blocks much more capable than yesteryear’s TDAxxxx chips, You can have a 8 pin iC with LNA ,mixer, IF and pin programmable filtering and gain for 3$, so while admirable and well beyond my electronics skill level, scratch building radios is for show off at ham fests.
Got links to candidate chips?
I’m always on the prowl for new things to play around with.
MICRF002 or SYN500R 350-450mhz. The latter is quite sensitive. Putting an LNA and a band passer filter in front of One of these, makes them as good a any full blown radio. They are data receivers, but the demodulated signal is available so is rssi.
looking at the datasheet, just combine with a microcontroller and you have a radio bbs
Both MICRF002 and SYN500R are rather integrated deals only making them useful for OOK/ASK receivers at 300-450MHz band. No access to the mixer output before integrated IF filters, no access to the IF filter outputs before it goes to built in demodulators. And the demodulators in both are for AM/OOK only making them useless for most amateur applications.
If suggesting Micrel/Microchip chips at least suggest versions that have external IF filters so hat you can add your own demodulators.
When I tested SYN115 transmitter it’s integrated VCO+PLL deal had really bad phase noise.
I was planing on using it as a tunable LO (put vxo in the reference xtal osc) for a 70cm DSB transceiver.
But the phase noise just was too much.
Sadly so, 10dBm trough a 3dB attenuator would have been the perfect level to drive an SBL-1 with.
So both the proposed receiver chipsets are unusable for CW or voice receivers as is.
With SYN500R it might be possible to recover AM modulated audio from the RSSI pin or by pushing the slicer level to something more useful. But that is just AM, no CW, SSB or FM.
Why are radio amateurs referring to frequencies in terms of wavelengts? Is it clinging to old terms? It’s annoying, use frequency in Hz like everyone else!
We do both. The 80m band (in the US) begins at 3.5 MHz.
Only IT people use MHz or GHz. Radio people use meters or centimetres (or manometers if you can see the radio waves)
Na just kidding. But f = c / λ, so use a calculator. Or your mind – 300MHz is a meter, so it’s easy to visualise it both ways at the same time. 600MHz is half a meter etc. Knowing the wavelength gives you a feel for what size aerial or waveguide you need, or how to layout the tracks going to your CPU (in which case you need to convert the bus speeds to wavelength anyways)
You think in terms of wavelengths when you’ve got to build an antenna, but frequency when you’re turning a knob. One gets used to it.
We refer to frequencies in wavelengths so we know how to calculate the length of our antennas.
Here’s a link: http://www.csgnetwork.com/antennaevcalc.html
Diverting the question by giving me lessons in first degree mathematics tells me you feel awkward about this You just like to talk about the size of your antennas, don’t you?
because at low frequency the size of your antenna becomes a very annoying problem to resolve. So you made a big bow tie with 160 meters of wire, now you just need some where to put it. yikes!
Referring to wavelength, or bands, is a convenient way of speaking in generalities. It’s like saying, “It’s springtime,” instead of quoting a specific date. Just knowing it’s springtime gives an expectation of what you might to see walking outside. Likewise knowing that a signal is on the 75 meter band, might provide you with some expectations of what you might hear there.
Probably for similar reasons as to why chemists (or at least infrared spectroscopists) forgo both frequency and wavelength and use wavenumbers instead…
This practice dates back to the very early history of the radio, when there were fixed tuning circuits and the produced and received frequency was obtained by using the right length antenna (which resonates just like a LC network) paired with rheostat-like matchers for fine tuning.
There are other challenges besides transistor capabilities to consider when moving to higher frequencies. And.. when you meet them all you are rewarded with very limited range due to lack of skip! And few people to talk to anyway because FM is more popular at small bandwidths than SSB.
Unless you want to talk through satellites….
I Think there’s a bag of 547’s from 30years ago somewhere around here probably 500 or so must be in a box.
There is a PCB layout for the VK3AJG transceiver in the wild that was done by G4USP:
http://www.qsl.net/g4usp/BC547%20HF%20TXCVR/All%20transistor%20BC547%20SSB%20HF%20TXCVR.htm
It’s in eagle binary format, but Eagle binary layouts can be loaded by the FLOSS PCB layout tool pcb-rnd – there’s a screenshot of the layout at:
http://vk5hse.blogspot.com.au/2017/12/importing-cadsoft-eagle-binary-layouts.html
Or loaded in to eagle 7.7, the last one before DRM requiring accounts and converted to the XML version.
About 20 years ago there was a project that designed a radio transceiver using nothing more than 2N2222 transistors as the active elements. You could use diodes of various kinds, but the amplification had to be done with the cockroach of transistors, the 2N2222. There were several entries. The one that won was known as the 2N2-40. See http://www.k8iqy.com/qrprigs/2n240/2n240page.html
My understanding was that BC547 is to our European friends what 2N2222 is to hobbyists in the western hemisphere. So.. yeah.. these two projects would very much be in the same spirit. If 2N2222 is an american cockroach then BC547 is a european cockroach.
Of course now with the internet.. 2N2222, BC547… who cares where you live?!?
So, it uses one type of device, and 28 of those devices.
The problem with these is that the other types of components are as difficult or more difficult to source than specialized transistors, like the ferrites, tunable caps and inductors, film caps, crystals, etc, etc. But yet they will always say they just got these parts out of their “garbage bin.” The one area where these designs DO add a lot of value is in paralleling the output transistors for more power, because discrete RF power transistors become harder to source and more expensive over time.
[Jenny List] is somewhat of an authority in this area. It seems she started with a
miss-spent youthhobby of scrapping old CRT TV sets and other electronics for parts to build her projects. This indicates that she has a lot of experience with discreet component level design.1) I don’t know of the specifics of the BC547 series as I really haven’t used them since the late 80’s or early 90’s but I certainly agree with here generalization about older designers. I can generally get a good idea about the age of a designer by looking at what part numbers they have used in the schematic.
Then there is the question of what obsolete really means. There is no such thing (as far as I am concerned) as a BC547A/B/C transistor or any other transistor by a number. The number itself represents a specification. Original transistors of a particular specification had very high device variations and that is reflected in the specifications. Transistors built with modern fab processes for high volume mainstream use have far less device variation and you will often find the actual specs of a device to be very close to the middle between Min and Max or at Typical.
On the other hand, when a number of people use old spec transistors but demand doesn’t make it to main stream quantities then the big manufacturers don’t bother to make them and that leaves a supply demand void which is often filled by China with transistors that are technically “close” to spec and cause a lot of problems especially with RF designs.
2) I don’t think that sentence is bad or insulting. It may be less true for younger engineers or designers but in [Jenny List]’s time it has been a given that you understand analogue. After all, when she started there wasn’t anything other than analogue.
So for an older person who started in the analogue era, you wouldn’t need to be a genius to build one and get it working to spec. But for younger people that don’t have an analogue background building it shouldn’t be a problem but debugging it and getting working to a specification may be challenging depending on the quality of the work done to build it.
it uses 2 types, 557’s and 547’s